The most popular black pigments in cosmetic products nowadays are carbon black and iron oxide black. Black iron oxide pigment, also known as ferrous ferric oxide (Fe3O4), consists of particles with diameters between about 1 and 100 nanometers. It has no known health hazards and is considered non-toxic. It is more opaque and less toxic than other black pigments.
Carbon black pigment is produced by the incomplete combustion of hydrocarbon gas or oil. It is an ultra black pigment, providing the most authentic black shades available. The benefits of carbon black for use in cosmetics and particularly in mascaras include less clumping, less beading, less buildup, better lash separation and better lash curling. Since carbon black is lighter with more color effect at low use concentrations, final formulations offer maximum cosmetic performance without caking and buildup.
However, carbon black has not been permitted for cosmetic use in the U.S. from 1976 to 2004. In 2004 the U.S. Food and Drug Administration (FDA) approved the use in cosmetics of one form of carbon black: high purity furnace black (one of the five types of carbon black which have been produced). The FDA named the allowed colorant D&C Black #2 to emphasize that the material is subject to batch certification.
In addition, carbon black is very difficult to handle during the process of manufacturing formulations. It consists of fine amorphous particles having an average primary particle size as small as 0.05 to 0.5 μm. Due to the fine primary particle size, carbon black particles tend to heavily aggregate and can be difficult to disperse uniformly in vehicles or resin compositions. In addition, carbon black particles have a very low bulk density (about 0.1 g/cm3) and, accordingly, can easily become airborne and contaminate the working environment.
Pigments, especially carbon black, present problems to customers trying to handle and disperse these products. Customers desire to have a product which is dust free, can be easily handled in conventional material transferring equipment and have the same product in a form that will easily disperse in the host formulation. Additionally, carbon black lacks significant surface functional groups, which means that the particles are hard to wet and therefore difficult to disperse.
Achieving an adequate dispersion involves imparting enough energy in the system to overcome attractive forces between particles without putting much energy in the system that can destroy or change the desired properties of the formulation. Achieving dispersions of particulate matter, and in particular carbon black dispersions, remains the domain of experience and know how.
The primary particle size of a carbon black particle determines, to a large extent, its degree of dispersibility. The smaller the primary particle the higher the surface area, resulting in more area to wet and thus requiring more energy than a carbon black particle having lower surface area. Additionally, as the carbon black aggregate becomes smaller there is a higher volume concentration of carbon black at the same weight loading (compared to particles having larger aggregates) resulting in smaller inter-aggregate distances and, consequently, greater attractive forces to overcome.
It would be beneficial to provide carbon black in an encapsulated form that would increase the safety of use, avoid dustiness during manufacturing of the composition, and improve dispersion of carbon black in the composition and will not be considered as a nanomaterial (1-100 nanometer).
U.S. Pat. No. 5,286,291 discloses pigments containing carbon black and having improved abrasion resistance. WO 2010/085689 discloses antimicrobial carbon black dispersions. U.S. Pat. No. 7,300,512 discloses a method of making pigment dispersion containing a carrier such as castor oil or vegetable wax, wherein the pigment is optionally black iron oxide.
U.S. Pat. Nos. 6,932,984 and 7,838,037 assigned to the same applicant of the present application disclose a method for microencapsulation of substances by the solvent removal method using non-chlorinated solvents. The method is based on physical processes only which do not cause any change of original physical and/or chemical properties, biological activity, and safety of raw materials during the process. This method affords physical stability of the microcapsules, high ability to entrap the active agents, protection of the active agents inside the microcapsules, and prevention of the diffusion of the microencapsulated active agents to the external water phase in a water-based preparation. In U.S. Pat. No. 7,838,037 the resulting microcapsules are double layer and triple layer microcapsules. WO 2009/138978 of the same applicant discloses cosmetic compositions comprising double layer microcapsules which contain black iron oxide with additional iron oxides.